1. Field of the Invention
The present invention relates to a lamp unit of a vehicle headlamp, particularly relates to a lamp unit of a projector type constituted to form a light distribution pattern having a cutoff line.
2. Related Art
In a background art, a lamp unit of a projector type is known as a lamp unit of a vehicle headlamp. The lamp unit of the projector type is constructed by a constitution including a projector lens arranged on an optical axis extended in a front and rear direction of a vehicle, a light source arranged on a rear side of a rear side focal point of the projector lens, and a reflector for reflecting light from the light source to a front side to be proximate to the optical axis. When a light distribution pattern having a cutoff line as in a light distribution pattern for low beam is formed by light irradiated from the projector type lamp unit, there is constructed a constitution of arranging a shade for shielding a portion of reflected light from the reflector at a position of the rear side focal point of the projector lens and a cutoff line is formed as an inverted projected image of an upper end edge thereof.
At that occasion, JP-A-03-122902 discloses a lamp unit of a projector type in which a surface of a projector lens is constituted by a small recessed and projected face. JP-A-2005-302718 discloses a lamp unit of a projector type in which a plurality of recessed and projected portions are formed on a surface of a projector lens thereof in a shape of concentric circles. JP-A-01-186701 discloses a lamp unit of a projector type in which an upper portion region and a lower portion region remote from an optical axis in an up and down direction are constituted to deflect light emitted from a projector lens in a lower direction at a surface of the projector lens.
When the light distribution pattern having the cutoff line is formed by light irradiated from the lamp unit of the projector type, the cutoff line is formed extremely clearly as the inverted projected image of an upper end edge of the shade. Therefore, light is hardly irradiated to an upper side of the cutoff line, and optical recognizability of a remote region of a vehicle front side road face is liable to be insufficient. In such a case, there is a concern of giving a useless strange feeling to a driver of a vehicle running on an opposed lane, since a spectroscopic color appears at a vicinity of an upper side of the cutoff lien by a spectroscopic phenomenon brought about when light from a light source reflected by the reflector transmits through the projector lens.
In contrast thereto, when the constitutions described in JP-A-03-122902 and JP-A-2005-302718 are adopted, the cutoff line can be shaded off by diverging light emitted from the projector lens, thereby, the spectroscopic color at an upper vicinity of the cutoff line can be made inconspicuous.
However, according to the projector lens described in JP-A-03-122902, since the surface is constituted by the small recessed and projected face, it is not easy to control a degree of diverging light emitted from the projector lens, the diverging is liable to be insufficient or excessive. There poses a problem that when the diverging is insufficient, the cutoff line is sufficiently shaded off or a countermeasure against the spectroscopic color at an upper vicinity thereof becomes insufficient. On the other hand, when the diverging is excessive, by diverging light by which a lower vicinity region of the cutoff line is to be formed, a brightness thereof is reduced, glare is liable to be cast to a driver running on an opposed lane since light diverged to an upper side of the cutoff line becomes excessively large.
According to the projector lens described in JP-A-2005-302718, since the surface is formed with a plurality of recessed and projected portions in the shape of concentric circles, a degree of diverging light emitted from the projector lens can accurately be controlled. However, the emitted light is diverged in a diameter direction relative to the optical axis of the projector lens. Therefore, there poses a problem that there is brought about variations in shading off the cutoff line or an effect of the counter measure against the spectroscopic color at the upper vicinity are brought about depending on a position from which light from the projector lens is emitted.
According to the projector lens described in JP-A-01-186701, the upper region and the lower region of the surface remote from the optical axis in the up and down direction are constituted to deflect light emitted from the projector lens in the lower direction. Therefore, light emitted from the region of increasing a spectroscopic degree can be concealed to a position on the lower side of the cutoff line. Thereby, the effect of the countermeasure against the spectroscopic color can be promoted. However, when constituted in this way, a clearness of the cutoff line is further promoted. Therefore, there poses a problem that with regard to the effect of shading off the cutoff line, an inverse effect is rather brought about.